A recent 1,200-mile East Coast road trip in my 2013 Tesla Model S electric car proved to be something of a turning point in my view of the car.

Fitted with the smaller 60-kilowatt-hour battery pack, my car s EPA range of 208 miles was not quite enough to make it between Superchargers—Tesla s proprietary ultra-fast DC charging stations—at normal Interstate speeds in cold weather.

I could extend the car s range by driving 60 mph in the slow lane, with the heat off, or loiter in the customer lounges of Nissan dealers along the way, while my car picked up the extra few miles it needed courtesy of their slower Level 2 charging stations.

Neither alternative turned out to be much fun.

Tesla Motors — Model S lithium-ion battery pack

And it was my first experience of buyer s remorse.

Not for buying a Model S—not at all—but for not ponying up the extra $8,000 to specify the larger 85-kWh version of the Model S, withan EPA range of 265 miles, which could have covered the distances between Superchargers with ease.

As I wrote at the time: Damn. Coulda, woulda, shoulda got the 85.

Well, it now appears that Fate has smiled upon me. In an example of exquisite timing, I received an unexpected end-of-year financial windfall. And my tax guy strongly recommended that I spend some of it before December 31.

Three upgrade options

Yes, sir! Anything you say, sir!

The way I saw it, there were three possible ways to upgrade my 60-kWh car to an 85-kWh version.

Swap out the 60-kWh battery in my car for a new 85-kWh battery

Trade in my car for a new 85-kWh model

Trade in my car for a similarly-equipped used 85-kWh Model S, of roughly the same age/mileage as mine.

Battery swap: We don t do that

I d seen the Tesla video of its prototype 90-second automated battery swapping system, which may or may not become a commercial reality one of these days.

But would Tesla do a one-time permanent battery upgrade for a customer?

2013 Tesla Model S electric sport sedan [photo by owner David Noland]

I called my local Tesla service center, in White Plains, New York.

Good question, came the reply. I ve never heard of anybody doing that—but we ll look into it and get back to you.

Being an impatient sort, I decided to call Tesla headquarters myself. The verdict from the factory service guy I talked to there was brief and clear: Sorry, we don t do that.

Okay. On to the second option.

Trade for a new one

The original list price of my car had been $73,000. A new Model S, identical to mine but with an 85-kWh battery instead of the 60, would today list at $83,500.

That s eight grand more for the bigger battery, plus an across-the-board $2,500 price increase that was levied on all orders placed this year (I d ordered my car considerably further in the past).

Tesla Motors — Model S lithium-ion battery pack

Add sales tax, delivery, preparation, and fees, and the total would come to about $88,500.

I called Tesla and was given a trade-in value for my car (nine months old, with 10,000 miles) of $49,900 today.

But the new car wouldn t be delivered for two months, and the additional age and miles on my car would cut my trade-in value at the time of delivery to about $46,000.

The $7500 Federal tax credit wouldn t kick for 15 months, in April 2015, but it would cut my net cost to $35,000. Still: Ouch.

On to the final option.

Trade for an inventory car

Tesla has a formula for setting the price of inventory models, which are store loaners or sales/marketing demonstration cars offered for sale.

2011 Chevrolet Volt and 2013 Tesla Model S [photo: David Noland]

Their new list price is reduced by 1 percent per month from the date of delivery, plus $1 per mile on the odometer.

By that formula, an 85-kWh equipped just like mine, with the same age and mileage, would cost $65,500. With my car worth $49,900, I d pay $15,600 to trade up—if I could find one.

That proved to be the rub. After I expressed interest in the deal, a Tesla sales rep was able to come up with only two standard 85-Kwh inventory cars (not the pricier Performance model). But both were very low-mileage, well-equipped cars that cost as much or more as the new one I d priced.

The sales rep told me that inventory cars were constantly becoming available—and if I waited long enough, I d probably be able to get something close to what I wanted.

Local service to the rescue

But I didn t want to wait indefinitely, watching my trade-in value decline by $2,000 a month. And I didn t want to end up paying for popular options I didn t want, like a moonroof or a premium sound system.

Then, to my surprise and delight, the White Plains service center called back with good news.

2013 Tesla Model S electric sport sedan [photo by owner David Noland]

Yes, they could, in fact, swap out my 60-kWh battery for an 85-kWh pack. And they could do it next week. The cost would be about $18,000.

My first question: Will this swap give me the full 85-kWh configuration, with its more powerful motor and slightly better performance?

Yes, I was assured, I d get that added kick. The motor and inverter systems in the two models are physically identical, I was told, but 60-kWh cars are software-limited to 302 horsepower, against 362 hp for 85-kWh cars. Why?

The smaller battery isn t safely able to deliver the necessary current to provide 362 hp.

A software tweak would boost my motor s output to 362 hp, and cut my 0-to-60-mph time from 5.9 to 5.4 seconds. Top speed would also increase by 5 mph, to 125 mph.

Money, money, money

Cost breakdown

The cost breakdown looked like this: Price of the new battery was $44,564. The trade-in value of my old battery was $29,681—a number arrived at by discounting its new list price of $37,102 by a 20-percent restocking fee.

I had hoped that the trade-in value of my old battery would be prorated for its actual use—10 months and 11,000 miles out of its guaranteed life of eight years and 125,000 miles. This would have amounted to about a 10-percent restocking fee rather than the actual 20 percent

But Tesla needs to make a profit on this transaction; I understand that.

The net cost to me of the new battery was $14,883. Adding five hours of labor ($600), minor parts ($125), the battery shipping cost ($1,520), and sales tax ($1,257) brought the grand total to $18,386.

I thought long and hard: Should I do this?

I remember my thought process from a year ago, while debating whether to buy the 60-kWh or 85-kWh battery. How often, I asked, would I have a trip that was more than 208 miles but less than 265? Not very often, I d answered.

Turns out I was wrong. But still, 18 grand is a lot of money for a little peace of mind.

In the end, I justified the expense to myself (and my wife) the same way I originally justified the $10,000 step up from the now-defunct 40-kWh Model S to the 60-kWh version: I ll get a good portion of that extra cost back in added value when I eventually sell or trade in the car.

2013 Tesla Model S P85 service loaner vehicle [photo: David Noland]

Quick and easy

The installation itself was routine. I dropped the car off on a Friday, and drove home in a P85+ loaner.

(Unfortunately, I couldn t have any real fun with this top-of-the-line loaner. At 25 degrees, its 21-inch high-performance tires were so hard and traction-free that even modest power broke the rear tires loose on dry pavement; I can only imagine how bad they d be on snow or ice.)

The battery swap, as well as a headlight upgrade, was done by Saturday morning; Tesla delivered the car back to me on Monday.

While it s fun to look at my Rated Range indicator and see 230 instead of 180, it may be months before I ll actually utilize my extra 50 or 60 miles of range. But that s okay.

I m now, finally, equipped as well as I can be to navigate the Great Northeast Supercharger Desert—my home for the foreseeable future.